The present invention relates to a novel gypsum-based composition suitable as a molding material.
Molding compositions giving the combined effects of the hydrualic reaction of low hydrated gypsum and the curing reaction of a synthetic resin have heretofore been obtained by kneading a mixture of half-hydrated gypsum powder and a synthetic resin such as urea-formaldehyde resin, phenol-formaldehyde resin, acryl resin, polystyrene resin and polyvinyl alcohol resin dissolved in water. However, when a previously prepared resin composition is kneaded, great improvement in strength due to the effect of curing the resin itself cannot be expected, so that there is a limitation to the strength attainable. Also, if it is intended to increase the strength, a very large quantity of resin should be used.
It is also known in the art to obtain a hardened product of high strength by the so-called impregnation method, in which gypsum is impregnated with a solution of a monomer, the resultant system being subsequently subjected to a step of thermal polymerization. This method, however, involves a number of steps and requires special equipment. Moreover, it is usually difficult to achieve sufficient impregnation with the monomer liquid, so that the lack of uniformity of strength inevitably results.